Process for the preparation of glycerol carbonate

Abstract

This invention relates to a process for the preparation of glycerol carbonate from the reaction of glycerol and a dialkylcarbonate, for example dimethyl carbonate, or a cyclic alkylene carbonate. More specifically, the invention relates to a process where the synthesis of glycerol carbonate is conducted in the presence of a homogeneous transesterification catalyst and involves the partial reaction of a glycerol reactant stream and a dialkyl carbonate or cyclic alkylene carbonate reactant stream and an intermediate step of alcohol by-product separation before further reaction in order to improve glycerol conversion and glycerol carbonate selectivity and yield.

The invention claimed is: 
     
       1. A process for preparing glycerol carbonate comprising the steps of:
 (i) in a first reaction zone in the presence of a homogeneous transesterification catalyst, contacting and partially reacting a glycerol reactant stream with at least one member of a group consisting of: a) a dialkyl carbonate reactant stream, comprising greater than 80 wt. % dialkyl carbonate, and b) a cyclic alkylene carbonate reactant stream, comprising greater than 80 wt. % cyclic alkylene carbonate; 
 (ii) separating at least a portion of the alcohol by-product formed from the reaction in step (i) from the reaction mixture so as to obtain an alcohol-containing by-product stream; 
 (iii) reacting at least a portion of the remaining reactants in a second reaction zone in the presence of the homogeneous transesterification catalyst; and 
 (iv) obtaining a glycerol carbonate product stream. 
 
     
     
       2. The process according to  claim 1 , wherein the glycerol reactant stream is combined with the homogeneous transesterification catalyst prior to being fed to the first reaction zone. 
     
     
       3. The process according to  claim 1 , wherein the homogeneous transesterification catalyst is present in the reaction mixture in an amount from at least one member of a group consisting of: 0.25 to 5 wt % based on the mass of glycerol fed to the first reaction zone, and from 0.5 to 1.5 wt %, based on the mass of glycerol fed to the first reaction zone. 
     
     
       4. The process according to  claim 1 , wherein contacting and reacting in step (i) achieves at least one member of a group consisting of: from 50 to 90% glycerol conversion, from 70 to 90% glycerol conversion, from 80 to 90% glycerol conversion, greater than 50 wt. % of the alcohol by-product is removed in step (ii), greater than 75 wt. % of the alcohol by-product is removed in step (ii), and greater than 95 wt. % of the alcohol by-product is removed in step (ii). 
     
     
       5. The process according to  claim 1 , wherein the molar ratio of dialkyl carbonate and/or cyclic alkylene carbonate to glycerol fed to the first reaction zone is in the range of 1:1 to 3:1, 1:1 to 2.0:1, or in the range of 1.1:1 to 1.4:1. 
     
     
       6. The process according to  claim 1 , wherein:
 a) at least one of the first and second reaction zones are operated at a temperature from at least one member of a group consisting of: 40 to 160° C., 60 to 140° C., and 80 to 120° C.; 
 b) the first reaction zone is operated at a pressure of at least one member of a group consisting of: from 10 kPa absolute to 1,500 kPa absolute (0.1 to 15 bar absolute), from 100 kPa absolute to 1,000 kPa absolute (1 to 10 bar absolute), and from 200 kPa absolute to 600 kPa (2 to 6 bar absolute); or 
 c) the second reaction zone is operated at a pressure of at least one member of a group consisting of: from 5 kPa absolute to 150 kPa absolute (0.05 to 1.5 bar absolute), from 10 kPa absolute to 100 kPa absolute (0.1 to 1 bar absolute), and from 15 kPa absolute to 50 kPa absolute (0.15 to 0.5 bar absolute). 
 
     
     
       7. The process according to  claim 1 , further comprising a step of introducing at least one member of a group consisting of: further dialkyl carbonate for reaction in the second reaction zone to replenish dialkyl carbonate lost during alcohol separation step (ii) and further cyclic alkylene carbonate for reaction in the second reaction zone to replenish cyclic alkylene carbonate lost during alcohol separation step (ii). 
     
     
       8. The process according to  claim 7 , further comprising the condition selected from at least one member of a group consisting of: the molar ratio of dialkyl carbonate is higher in the second reaction zone than in the first reaction zone and cyclic alkylene carbonate to glycerol is higher in the second reaction zone than in the first reaction zone. 
     
     
       9. The process according to  claim 1 , wherein the process comprises continuous removal of alcohol by-product as it is formed in the second reaction zone. 
     
     
       10. The process according to  claim 1 , comprising at least one of:
 a) the dialkyl carbonate reactant stream comprises:
 i) greater than 90 wt. % dialkyl carbonate; 
 ii) less than 5 wt. % alcohol; and 
 iii) less than 2 wt. % water; and 
 
 b) the cyclic alkylene carbonate reactant stream comprises:
 i) greater than 90 wt. % cyclic alkylene carbonate; 
 ii) less than 5 wt. % alcohol; and 
 iii) less than 2 wt. % water. 
 
 
     
     
       11. The process according to  claim 1 , wherein the process further comprises a step of recovering the homogeneous transesterification catalyst from the glycerol carbonate product stream using a cation exchange resin. 
     
     
       12. The process according to  claim 1 , wherein a stream comprising an azeotropic mixture of dialkyl carbonate reactant/cyclic alkylene carbonate and by-product alcohol is obtained as a result of the process; wherein the process further comprises a step of separating the unreacted dialkyl carbonate/cyclic alkylene carbonate from the azeotropic mixture to form a dialkyl carbonate/cyclic alkylene carbonate recycle steam; and wherein the dialkyl carbonate/cyclic alkylene carbonate recycle stream is used as a source of dialkyl carbonate/cyclic alkylene carbonate reactant for the process. 
     
     
       13. The process according to  claim 1 , further comprising at least one of:
 a) a dialkyl carbonate reactant stream is employed in the process, wherein the dialkyl carbonate reactant is selected from dimethyl carbonate, diethyl carbonate or mixtures thereof; and 
 b) a cyclic alkylene carbonate reactant stream is employed in the process, wherein the cyclic alkylene carbonate is of Formula I below: 
 
       
         
           
           
               
               
           
         
         
           wherein: 
           R 1  is a divalent group, —(CH 2 ) n —, wherein n is an integer of from 2 to 6, and which is unsubstituted or substituted by at least one C 1  to C 6  alkyl group. 
         
       
     
     
       14. The process according to  claim 1 , wherein the homogeneous transesterification catalyst is selected from alkali metal carbonate, alkali metal bicarbonate, alkali metal hydroxide, alkali metal oxide, alkali metal alkoxide, alkali metal aluminate, alkali metal silicate alkaline earth metal carbonate, alkaline earth metal bicarbonate, alkaline earth metal hydroxide, alkaline earth metal oxide, alkaline earth metal alkoxide, alkaline earth metal aluminate, alkaline earth metal silicate or combinations thereof. 
     
     
       15. The process according to  claim 14 , wherein the homogeneous transesterification catalyst is selected from NaOMe, CaO, NaAlO 2 , Na 2 SiO 3  or combinations thereof. 
     
     
       16. The process according to  claim 1 , wherein the homogeneous transesterification catalyst is a basic ionic liquid of the formula:
   [Cat + ][X − ] 
 wherein: [Cat + ] represents one or more cationic species; and
 [X − ] represents one or more basic anionic species; 
 
 wherein: [Cat + ] comprises:
 a) an acyclic cation selected from:
   [N(R a )(R b )(R c )(R d )] + , [P(R a )(R b )(R c )(R d )] + , and [S(R a )(R b )(R c )] + , 
 
 
 wherein: R a , R b , R c , and R d  are each independently selected from a C 1  to C 30 , straight chain or branched alkyl group, a C 3  to C 8  cycloalkyl group, or a C 6  to C 10  aryl group; and wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: C 1  to C 6  alkoxy, C 3  to C 8  cycloalkyl, C 6  to C 10  aryl, C 7  to C 10  alkaryl, C 7  to C 10  aralkyl, —CN, —NO 2 , —C(S)R x , —CS −2 R x , —SC(S)R x , —S(O)(C 1  to C 6 )alkyl, —S(O)O(C 1  to C 6 )alkyl, —OS(O)(C 1  to C 6 )alkyl, —S(C 1  to C 6 )alkyl, —S—S(C 1  to C 6 alkyl), —NR y R z , or a heterocyclic group, wherein R x , R y  and R z  are independently selected from hydrogen or C 1  to C 6  alkyl; 
  or
 b) an aromatic heterocyclic cationic species selected from: benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, diazabicyclodecenium, diazabicyclononenium, diazabicyclo-undecenium, dithiazolium, imidazolium, indazolium, indolinium, indolium, oxazinium, oxazolium, iso-oxazolium, oxathiazolium, phthalazinium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, triazinium, triazolium, and iso-triazolium; 
 
 and wherein: [X − ] comprises an anion selected from alkyl carbonate, hydrogen carbonate, carbonate, hydroxide, alkoxide, chloride, bromide, nitrate and sulphate. 
 
     
     
       17. The process according to according to  claim 16 , further comprising at least one of:
 [Cat + ] comprises a cation selected from: 
 
       
         
           
           
               
               
           
         
         and 
         [X − ] comprises an anion selected from alkyl carbonate. 
       
     
     
       18. The process according to  claim 17 , wherein [X − ] comprises an anion selected from [MeCO 3 ] − . 
     
     
       19. The process according to  claim 1 , wherein the homogeneous transesterification catalyst is:
 a) an organic acyclic amine selected from tert-butylamine, isopropylamine, triethylamine, ditertbutylamine, diisopropylamine, diisopropylethylamine, dicyclohexylamine, dibenzylamine, benzyldimethylamine, diacetylchlorobenzylamine, dimethylphenethylamine, 1-dimethylamino-2-phenylpropane and N,N,N′-tritert-butylpropanediamine; or 
 b) a substituted piperidine derivative having two to six C 1 -C 4  alkyl substituents and where at least two of the alkyl substituents are located on carbon atom(s) adjacent the nitrogen atom of the ring. 
 
     
     
       20. The process according to  claim 19 , wherein the homogeneous transesterification catalyst is selected from 1,2,6-trimethylpiperidine, 2,2,6-trimethylpiperidine, 2,2,6,6-tetramethylpiperidine, 2,2,4,6-tetramethylpiperidine, 2,2,6,6-N-pentamethylpiperidine.